(1) Technical Field
The technology presented herein relates to a laser fixing device for use in an image forming apparatus based on electrophotography and an image forming apparatus including this laser fixing device.
(2) Description of the Prior Art
As fixing devices used for image forming apparatuses based on electrophotography such as copiers, printers, etc., fixing devices of heat roller fixing types are often used. A fixing device of a heat roller fixing type includes a pair of rollers (fixing roller and pressing roller) being pressed to each other, and is configured such that one or each of these rollers incorporates a halogen heater etc. so as to heat the pair of rollers to a predetermined temperature (fixing temperature) and a recording sheet with an unfixed toner image formed thereon is fed to and passed through the pressing contact (fixing nip portion), whereby the toner image is fixed with heat and pressure.
However, in the conventional heat roller type fixing device of this kind, it takes a long warm-up time to raise the temperature of the fixing roller and pressing roller to the predetermined fixing temperature, so that it is necessary to pre-heat the fixing roller and pressing roller also in the standby mode, hence posing the problem of power consumption being increased.
In order to solve this problem, a laser type fixing device that performs a fixing process by irradiating the unfixed toner image formed on the recording paper with laser beams emitted from laser elements arranged in a row to fuse and fix the toner image has been proposed in Patent Document 1 (Japanese Patent No. 3016685) and others. However, this method has the problem that if some of laser elements have broken down, there occur areas where a sufficient amount of irradiation with laser beams for fixing cannot be obtained.
To deal with this, Patent Document 2 (Japanese Patent Application Laid-open H07-191560) discloses a technology in which laser beams from multiple laser emitters are radiated on one area of the recording paper in an overlapping manner so as not to cause any unfixed area even if some laser elements have broken down.
However, even if laser beams from multiple laser emitters are arranged so as to irradiate in an overlapping manner and compensate for the reduction of the amount of irradiation by the neighboring laser elements if a laser element has broken down, there is a possibility to cause partial fixing failure and/or gloss unevenness due to difference in intensity of irradiated energy when a large amount of toner is supplied and adhered, for example, in a multi-layered color image.
The present technology has been devised in view of the above conventional problems, it is therefore a feature of the present technology to provide a laser fixing device that can provide a stable performance in toner fixing even when some laser elements have broken down as well as providing an image forming apparatus including this laser fixing device.
The example embodiment presented herein resides in a laser fixing device for fusing and fixing a toner image formed on a recording medium, to the recording medium by irradiating the toner image with laser light, comprising: a laser array module having a plurality of laser elements arrayed therein; a defective laser element detector for detecting a defective laser element; and, a controller which, when a defective laser element is detected by defective laser element detector, increases the power of laser elements that can radiate laser light on areas overlapping with the area of irradiation of the defective laser element in order to compensate for reduction in irradiation intensity in that area.
In the above way, the loss of irradiation intensity due to the broken laser element is compensated by the neighboring laser elements so as to enable uniform laser irradiation, making it possible to alleviate local fixing failure and gloss unevenness.
The laser fixing device is further characterized in that the controller sets up compensating conditions for the laser elements to be increased in power, in accordance with the area to be irradiated, the amount of irradiation and the timing for irradiation.
In this way, since the optimal compensation conditions are set up in accordance with the area of irradiation, the amount of irradiation that can be compensated and the irradiation timing, it is possible to constantly provide stable fixing performance.
The laser fixing device is further characterized in that the controller selectively uses laser elements to be increased in power, depending on the degree of degradation of the irradiating intensity of the defective laser element.
In this way, since the laser elements to be used for compensation are selected depending on the degree of degradation of the defective laser element, this makes it possible to markedly alleviate the shortening of the life of the normal laser elements.
The laser fixing device is further characterized in that when having determined that the defective laser element cannot be compensated for by other laser elements, the controller limits the recording mediums to the size at which the defective laser element will not be involved in fixing.
In this way, even when compensation by laser irradiation from those other than the defective laser element is impossible, the functions to be suspended can be minimized so as to keep user's loss of convenience to a minimum.
The laser fixing device is further characterized in that when having determined that the defective laser element cannot be compensated for by other laser elements, the controller switches the conveying speed of recording mediums to a lower speed so as to acquire the necessary amount of irradiation for compensation.
In this way, even when compensation by laser irradiation from those other than the defective laser element is impossible, it is possible to keep user's loss of convenience to a minimum by enabling a fixing process, though the conveying speed of the recording paper is lowered.
The laser fixing device is further characterized in that the laser array module is formed of one or more arrays arranged in the conveying direction of recording mediums, each having a row of laser elements arranged in the perpendicular direction to the conveying direction, and the compensating controller uses the laser elements, of the array to which the defective laser element belongs and, of the other arrays.
In this way, the burden for compensation is shared by a number of normal laser elements so that it is possible to reduce the burden on individual laser elements. Accordingly, it is possible to obtain preferable performance without notable loss of the life of the laser elements.
The laser fixing device is further characterized in that the defective laser element detector performs fault decision when no job operation is performed.
The present embodiment resides in an image forming apparatus comprising: a photoreceptor drum having the surface on which an electrostatic latent image is formed by irradiation with light; a light exposure unit that irradiates the photoreceptor drum with the light to form the electrostatic latent image; a developing unit that supplies toner to the electrostatic latent image on the photoreceptor drum surface to form a toner image; a transfer device for transferring the toner image from the photoreceptor drum surface to a recording medium; and, a fixing device for fixing the transferred toner image to the recording medium, wherein the fixing device employs the laser fixing device described above.
According to the present embodiment, the loss of irradiation intensity due to the broken laser element is compensated by other laser elements so as to enable uniform laser irradiation, making it possible to alleviate local fixing failure and gloss unevenness. Further, even when compensation by laser irradiation from those other than the defective laser element is impossible, it is possible to continue a fixing process though it is conditional, hence keep user's loss of convenience to a minimum.